The long term objectives of the proposed research are to elucidate some of the factors that control differentiation and development in the early mammalian embryo. There have been few studies of the effects of growth factors on early mammalian embryos. Following the observation that insulin binding to the mouse embryo is first detected at the morula stage, we propose to test the hypothesis that receptors capable of binding insulin appear first at the 16-cell stage of mouse embryogenesis (and comparable stages in other species) by using appropriate recombinant DNA probes and other molecular techniques. These will reveal the ontogeny of the insulin receptor and/or the receptor for the related insulin-like growth factor I (IGF-I). Functional studies to examine the significance of insulin and IGF-I binding include effects on nucleic acid synthesis and protein phosphorylation. Ultrastructural studies will be carried out of examine the mode of cytoplasmic entry and translocation of the receptor-ligand complex. These studies are expected to illuminate the involvement of insulin-like growth factors in early mammalian development, and may, in addition, extend knowledge of diseases where insulin is deficient.